"Amnesty Box," by Tim McLoughlin, in Alcohol, Tobacco, and Firearms, Akashic Press, 2022.This is a collection of stories and essays. If I am reading the acknowledgements correctly, this story is one of three new ones.
It is sometimes poor form for a reviewer to reveal that a story has an unreliable narrator. But since McLoughlin's character begins by saying "Appearance is everything and I'm a fraud" I don't think I'm giving away any secrets.
The protagonist is a postal service police officer in New York City. One reason he describes himself as a fraud is that he can accurately say he has been shot twice, in combat and on the job, but this ignores the fact that they were both minor injuries caused by friendly fire. Not as heroic as it sounds.
But the main thread of the story is a stunt he creates to speed up the occasional metal detector check which they run on post office customers, always on Friday because that is the lightest work day. You see, nobody want to spend the beginning of their weekend processing a bust.
Arrests go down on weekends, they go down in nice weather, they go down when they are inconvenient. Conversely, they spike shortly after Halloween and remain high through Thanksgiving, when overtime checks will arrive in time for Christmas shopping.
The cop invents the Amnesty Box, explaining that customers can drop into this cardboard box anything they know they shouldn't be taking through the metal detector. The catch is they won't get the dumped items back. "Even on a slow day we would collect a couple small bags of weed and a few knives."
A harmless-enough trick until something much more dangerous is dumped in the box. Then the story takes several surprising turns...